Solutions and Solubility
Essential Questions
1. What’s a solution vs mixture?2. What’s the difference between a solution,
solvent and solute?3. Can do you quantify concentration?4. What do some things dissolve while
others do not?5. How can we increase the rate that
something dissolves?
What happens when stuff dissolves?
http://www.youtube.com/watch?v=0cPFx0wFuVs
Mixtures and Solutions
Remember back to the beginning of the year when we learned about mixtures!
Concept check: Identifying Mixtures
Identify the follow as homo or heterogenous:Milk OilMuddy water IronBrass BloodPaint WaterSoda Sugar waterFlat Soda Toothpaste
Heterogeneous Mixtures
There are two types of heterogeneous solutions: Suspensions: mixtures containing particles that
will settle out if left undisturbed. Examples: oil and water, sandy water, muddy water,
paint, and flour in water
Colloids: mixtures of smaller sized particles that do not settle out on their own
Examples: milk, blood, butter, smoke, spray deodorant, motor oil
Homogenous Mixtures
Also called solutionsCan be solids, liquids or gasesSingle phaseRemain mixed; particles DO NOT settle outCannot be separated by filter paper
Solutions
A solution is formed when a solute dissolves in a solvent forming a homogeneous mixture
Solutions
Solvent – present in the greatest amount
Solute – present in the lesser amountSolution – Mixture of 2 or more
substances that are a mixed homogeneously
Identify the solvent and solute?
Solution Solvent SoluteFlat Soda Water Sugar syrupLemonade Water Lemonade mix
Alloy like brass Copper Zinc
Air Nitrogen Oxygen
Antifreeze Water Antifreeze
Ocean Water Water salt
Antifreeze Close up
In 1885 Karl Benz of Germany invited the first radiator for cars
Before this, car engines were cooled with water and needed to be constantly refilled!
Antifreeze has ethylene glycol added to water to elevate the boiling point and depress the freezing point
Solvent Joke
WATER AS A SOLVENT
Water is the most effective solventWater will dissolve many ionic
compounds and most polar covalent compounds
Water is not effective as a solvent for non-polar covalent compounds
Effectiveness of water is because water is highly polar with hydrogen bonds
WATER AS A SOLVENT-HYDROGEN BONDING
Polarity Demonstration
Image used courtesy of CINCH ® Learning
The bond formed between an oxygen atom from one water molecule and a hydrogen atom from another water molecule
Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g-6m99vd692fc7hgidt985ta0?old_view=True
Concentration
The concentration of a solution is usually described as concentrated or dilute
There are many ways to express concentration:
Concentration as Percent by Mass
Ratio of the solutes mass to the mass of the solution expressed as a percentage!
Amount of solution = solute + solvent
percent by mass = amount of solute x 100 amount of solution
Concentration as percent by mass
1) What is the percent by mass if 2 grams of sugar is added and dissolved in 10 grams of water?
16.7%
Concentration as percent by mass
2) In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution?
3.5%
Concentration as MOLARITY
Another common unit of concentration used by chemist is molarity
Molarity = the solutions concentration measured as moles of solute per liter of solutionMolarity = Moles of solute
Liters of solutionUnits of M = Moles / Liter
Concentration as Molarity
1) How much sucrose, in moles, is there in 0.5 liters of a 2-molar (2M) solution?
1 mole
Concentration as Molarity
2) To make a 4.0 M solution, how many moles of solute will be needed if 12 L of solution are required?
Concentration as Molarity
3) 116.88 grams of NaCl are dissolved in 1.5 liters of solution. What is the molarity of this solution?
First, convert grams of NaCl to moles NaCl Found by dividing 116.88g by the molar mass of NaCl,
58.44 g/mol 116.88g NaCl is 2.00 moles of NaCl
Next, divide moles solute by liters of solution 2.00 moles NaCl = 1.33 mol NaCl/L = 1.33 M NaCl
1.5 L
Practice
Try the following calculating concentration as percent by mass and molarity problems
Dilution
What does it mean to dilute a solution?
Dilution
In the lab, sometimes reactions call for different strengths or concentration of solutions in order for a reaction to occur.
We use molarity to create solutions with the proper concentrations.
Often we need to dilute a stronger solution to a weaker one.
DILUTION
Solutions can be diluted simply by adding more solvent and leaving the amount of solute unchanged
What happens to molarity when a solution is diluted? More water has been added, so the total
volume of solution is greater but the amount of solute is the same
Molarity will decrease!
Dilution
We use the following equation to perform dilution calculations:
M1V1=M2V2
M1=Initial molarity
V1= Initial volume
M2= Final molarity
V2=Final volume
DILUTION EXAMPLE1) What would be the resulting molarity of
2.500 L solution when the starting solution had a molarity of 6.00 M and a volume of 417 mL?
M1= 6.00 mol/L M2= ?? V1= 417 mL V2= 2500 mL
M1V1=M2V2
(6.00 mol/L)(417 mL) = (M2)(2500 mL)
(M2) = (6.00 mol/L)(417 mL)
(2500 mL) M2 = 1.00 mol/L
Dilution
2) If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it?
0.19 M (the final volume is 900 mL, set up the equation from that)
STOP
Work on some problems on your own
CONCENTRATION AND SOLUBILITY
The amount of solute affects both solubility and dissolving rate.
A solvent can only dissolve so much solute.
As the concentration increases, the ability to dissolve more decreases, as does the rate at which it will dissolve.
Solution Concentration
Unsaturated When the amount of solute is less than the
maximum that could be dissolved
Saturated When a solution holds the maximum amount of
solute
Fats!
You’ve all heard that we should avoid saturated fats…so what does that mean? Saturated fats (butter, dairy products, meat) are
solid at room temperature and are evenly filled out with hydrogen. They increase the levels of bad cholesterol (LDL) and clog your arteries.
Mono and poly unsaturated fatty acids (corn oil, sunflower oil, and soybean oil, while omega 3 is present in salmon, trout and tuna) remain liquid at room temp and increase the levels of good cholesterol!
Solution Concentration
Supersaturated When a solution holds more than the maximum
amount and is thus unstable!
Supersaturated demohttp://www.youtube.com/watch?v
=1y3bKIOkcmk
SOLUBILITY CURVES
Show the amount of solute that can dissolve in a solvent under normal circumstances at a given temperature
The line for a given element on a set of solubility curves is called the saturation line
Factors affecting Solvation (aka rate of Dissolving)
Solvation: The act of surrounding solute particles with solvent particles to form a solution!
The solute is being pulled apart and surrounded by the solvent. Soluble – if you can dissolve any of the solute Insoluble – if you can’t dissolve any
We can change this by changing many different factors!
Factors Affecting SolvationThe rate at which the solute dissolves in the
solvent (link to KMT) As Kinetic Energy increases, dissolving rate
increases As Kinetic Energy decreases, dissolving rate
decreases As the number of collisions increases, dissolving
rate increases As the number of collisions decreases, dissolving rate
decreases
(1) TEMPERATURE AND DISSOLVING RATE
Increasing the temperature speeds up the movement of its particles
Allows for more collisions between solute particles and solvent particles
(2) SURFACE AREA AND DISSOLVING RATE
Breaking a solid into smaller pieces greatly increases its surface area
More solvent particles can come into contact with more particles of the solute corresponding to increased surface area
Rate of collisions increases as surface area increases
(3) AGITATION AND DISSOLVING RATE
Agitation
Stirring, Mixing, Shaking As agitation speed increases, rate of
dissolving increases As the solvent moves around, more
collisions occur between solvent and solute particles
SUMMARY OF FACTORS AFFECTING DISSOLVING RATESAs temperature ↑, dissolving rate ↑
As particle size ↓, surface area↑, dissolving rate ↑
As agitation ↑, dissolving rate ↑
LAB
Factor’s affecting solubility lab
SOLUTIONS & SATURATIONUnsaturated Saturated Super-
saturatedDefinition More solute can
dissolve in the solvent
No more solute will dissolve in the solvent. If there is extra undissolved solute, it will settle to the bottom of the container.
Under unusual circumstances more solute is dissolved in solvent than it can normally hold
Solubility Curve
Below the saturation line
On the saturation line
Above the saturation line
Can you Dissolve More Solute?
Yes No No, it is already past saturation point
SOLUBILITY CURVE
Let’s practice reading a solubility curve!
FACTORS AFFECTING SOLUBILITY
1. Temperature2. Pressure3. Polarity
FACTORS AFFECTING SOLUBILITY
(1) Temperature Solids and Liquids: Generally, as temperature
increases, the solubility of solids and liquids increases – why?
As temperature ↑, solubility ↑
Gases: Generally, as temperature increases, the solubility of gases decreases – why?
As temperature ↑, solubility ↓
FACTORS AFFECTING SOLUBILITY
(2) Pressure Solids and Liquids: no effect – why?
As pressure ↑, solubility is unaffected
Gases: Generally, as pressure increases, the solubility of gases increases – why?
As pressure ↑, solubility of gases ↑
FACTORS AFFECTING SOLUBILITY(3) Polarity!!
The nature of the solvent affects solubility Like Dissolves Like
Ionic compounds, if they are soluble, dissolve in polar solvents
Polar molecular (covalent) compounds dissolve in polar solvents
Non-polar molecular (covalent) compounds dissolve in non-polar solvents